Seasonal Fluctuations in the Selected Temperature of Speckled Trout, Salvelinus fontinalis (Mitchill)

Abstract

The selected temperature of two- to three-inch trout (Salvelinus fontinalis, Mitchill) was determined in a horizontal gradient a number of times during the months of November, December, January, February and March. The data, which were collected over four years, indicated that during the early part of winter (November, December and January), there was a fall of the selected temperature which paralleled in a general way a gradual fall of the acclimation temperature. The consistency of this parallelism was so poor, however, as to suggest that at least part of the change in selected temperature was relatively independent of the change in acclimation temperature. During the later part of the winter (February and March) there was a rise of the selected temperature which occurred regularly, regardless of whether the acclimation temperature rose, fell or remained constant. It is concluded that there was, for these animals, a seasonal change of the selected temperature which was distinct from the changes in selected temperature brought about by changes of the acclimation temperature.